In the HARQ (Hybrid Automatic Repeat Request) manner, codes sent by a transmitting end not only can detect errors but also have some error correction capability. A decoder at a receiving end, after receiving the codeword, firstly detects a error condition, if it is within the error correction capability of codes, then error correction will be carried out automatically, and if there are many errors which exceed the error correction capability of codes, but the errors can be detected, then the receiving end sends a judgment signal to the transmitting end through a feedback channel to require the transmitting end to re-transmit the information. In the OFDM (Orthogonal Frequency Division Multiplex) system, correct/wrong transmission is indicated by an ACK/NACK (Acknowledgment/negative-acknowledgement) control signaling so as to judge whether re-transmission is needed.
The long term evolution (LTE for short) system is an important plan of the 3rd Generation Partnership Project organization. FIG. 1 shows a structural diagram of a basic frame structure in an LTE system, and as shown in FIG. 1, the frame structure is divided into five levels of radio frame, half-frame, subframe, timeslot and symbol, wherein, the length of one radio frame is 10 ms, one radio frame is composed of two half-frames, the length of each half-frame is 5 ms, one half-frame is composed of 5 subframes, the length of each subframe is 1 ms, one subframe is composed of two timeslots, and the length of each timeslot is 0.5 ms.
When the LTE system adopts a normal cyclic prefix, one timeslot includes 7 uplink/downlink symbols with the length of 66.7 us, wherein, the cyclic prefix length of the first symbol is 5.21 us, and cyclic prefix length of other 6 symbols is 4.69 us.
When the LTE adopts an extended cyclic prefix, one timeslot includes 6 uplink/downlink symbols with the length of 66.7 us, wherein, the cyclic prefix length of each symbol is 16.67 us.
In the downlink HARQ of the LTE, an ACK/NACK response message of a physical downlink shared channel (PDSCH for short), when a user equipment (UE for short) is not transmitting physical uplink shared channel (PUSCH for short), is sent on a physical uplink control channel (PUCCH for short). The LTE defines a plurality of PUCCH formats, including PUCCH format 1/1a/1b and format 2/2a/2b, wherein format 1 is used for sending a scheduling request (SR for short) of the UE, formats 1a and 1b are used for feeding back a 1-bit ACK/NACK response message and a 2-bit ACK/NACK response message respectively, format 2 is used for sending downlink channel states indication (CSI for short) including CQI (channel quality indicator), PMI (precoding matrix indicator) and RI (rank indicator), format 2a is used for sending CSI and a 1-bit ACK/NACK response message, and format 2b is used for sending CSI information and a 2-bit ACK/NACK response message, and format 2a/2b is only used in a scenario that the cyclic prefix is the normal cyclic prefix.
In which, the channel structures of format 1, format 1a and format 1b are the same; format 1 multiplies a fixed modulation symbol 1 on the data symbol, and whether there is the SR information to be sent is transmitted based on whether there is the format 1 channel used for transmission; format 1a multiplies a BPSK (Binary Phase Shift Keying) symbol on the data symbol, and the transmitted BPSK symbol corresponds to the ACK/NACK of a single codeword; format 1b multiplies a QPSK (Quadrature Phase Shift Keying) symbol on the data symbol, and the transmitted QPSK symbol corresponds to the ACK/NACK of a dual-codeword; the channel structures of format 2, format 2a and format 2b are the same; format 2 transmits the CSI information on the data symbol, and the pilot (reference signal) symbol does not carry information bit; format 2a transmits the CSI information on the data symbol, and multiplies a BPSK symbol on the pilot (reference signal) symbol corresponding to the ACK/NACK to a single codeword; format 2b transmits the CSI information on the data symbol, and multiplies a QPSK symbol on the pilot (reference signal) symbol corresponding to the ACK/NACK to a dual-codeword; and the 2-bit information transmitted by the PUCCH format 1b is defined as b(0) and b(1).
In an LTE time division duplex system, two ACK/NACK feedback modes are supported. One is ACK/NACK bundling, the main idea of the feedback mode is to carry out a logic ‘AND’ operation on the ACK/NACK of the codeword corresponding to each downlink subframe which is fed back in the uplink subframe, if one downlink subframe has 2 codewords, the UE needs to feed back 2-bit ACK/NACK, and if each subframe only has one codeword, then the UE needs to feed back 1-bit ACK/NACK. The other is ACK/NACK multiplexing mode, the core concept of that feedback mode is, by using different PUCCH channels and different modulation symbols on the channel, to represent different feedback states of the downlink subframe which are fed back in the uplink subframe, if there are a plurality of codewords on the downlink subframe, firstly to carry out a logic ‘AND’ (also referred to as spatial bundling) operation on the ACK/NACK fed back by the plurality of codewords of the downlink subframe, then select one PUCCH channel and the corresponding 2-bit information b(0)b(1) carried on that channel in light of an agreed rule between both the base station and the user equipment and according to the ACK/NACK of each downlink subframe after carrying out the codeword logic ‘AND’ operation, and finally send the corresponding 2-bit information b(0)b(1) by using the PUCCH format 1b and on the selected PUCCH channel. That is to say, the ACK/NACK after carrying out the logic ‘AND’ operation between codewords is represented by the 2-bit information b(0) and b(1) carried by the PUCCH format 1b and the index of the PUCCH channel. Since in that method, the ACK/NACK of different downlink subframes are represented by selecting different PUCCH channels, the method can also be referred to as a channel selection.
In order to meet the requirement of the International Telecommunication Union-Advanced (ITU-Advanced for short), the long term evolution advanced (LTE-A for short) system as the evolution standard of LTE needs to support larger system bandwidth (up to 100 MHz), and needs to be backward compatible with the existing standard of the LTE. On the basis of the existing LTE system, the bandwidth of the LTE system can be combined to obtain larger bandwidth, and this technology is referred to as a carrier aggregation (CA for short) technology, which can enhance the frequency spectrum utilization rate of the IMT-Advance system and mitigate the lack of frequency spectrum resources, thereby optimizing the use of frequency spectrum resources.
When the LTE-A adopts the carrier aggregation technology, and when the UE is configured with 4 downlink component carriers, the UE needs to feed back the ACK/NACK of these 4 downlink component carriers. If in the MIMO situation the UE needs to feed back the ACK/NACK of each codeword, then, when the UE configures 4 downlink component carriers, the UE needs to feed back 8 ACK/NACK. At present, for the LTE-A system, there are mainly two solutions discussed for sending a plurality of ACK/NACK response messages: one is a solution based on the channel selection, and the other is a solution based on DFT-s-OFDM (Discrete Fourier Transform spread Orthogonal Frequency Division Multiplexing). FIG. 2 gives a schematic diagram of a solution based on the DFT-s-OFDM. In the schematic diagram, the ACK/NACK bit(s) needed to be fed back is mapped on the corresponding symbol(s) for sending information bit(s) after channel encoding, scrambling, modulating and DFT transforming, and then sent out by forming a subframe with a reference signal (RS). Since the DFT transform is used during the signal processing of the transmitting end, the manner is referred to as a solution based on the DFT-s-OFDM. However, at present there is still no conclusion about how to specifically determine the sending method of the ACK/NACK.